1. For each pair of conditions below, predict which reaction will be faster if t

Question

1. For each pair of conditions below, predict which reaction will be faster if the mechanism follows a SN2 pathway and give the reason for your answer. A)(a) substitution by iodide ion on CHC (b) substitution by iodide ion on CH OTs (Ts tosylate) B) (a) substitution by acetate ion (CH,COO) on bromoethane (b) substitution by acetate ion (CH,COO) on bromocyclohexane C)(a) substitution on 2-bromopentane by Eto (b) substitution on 2-bromopentane by NC D)(a) substitution by acetylide ion on bromomethane in benzene (b) substitution by acetylide ion on bromomethane in HMPA What is the major organic product(s) in the reaction of 1-bromopropane with the following reagents? 2. a) NaNH2 b) NaCN c) (CHal COK d) Nal

Explanation / Answer

1)

A) b. because OTs is a better leaving group than Cl-

B) a. due to less steric hindrance in bromoethane

C) a. EtO- is more nucleophilic than CN-

D) b. SN2 reaction occurs faster in polar aprotic solvent hence reaction occurs faster with HMPA

2)

CH3-CH2-CH2-Br + NaNH2 -----> CH3-CH=CH2

Since NaNH2 is a strong base it eliminates HBr from alkyl halides to form alkene

CH3-CH2-CH2-Br + NaCN ------> CH3-CH2-CH2-CN

CN- is nucleophile and hence it froms a substituted product

CH3-CH2-CH2-Br + (CH3)3COK ----> CH3-CH=CH2

Since (CH3)3COK is a strong base it eliminates HBr from alkyl halides to form alkene

CH3-CH2-CH2-Br + NaI ----> CH3-CH2-CH2-I + NaBr

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